This invention relates generally to controlling compressed feed gases and more particularly to controlling the pressure at the inlet of a fuel cell or other device utilizing a compressed gas feed.
Electrochemical conversion cells, commonly referred to as fuel cells, produce electrical energy by processing reactants, for example, through the oxidation and reduction of hydrogen and oxygen. The gases are often introduced into the fuel cells from pressurized storage tanks.
Mechanical pressure regulators have been used to control the pressure at the inlet to the fuel cell or other device. However, mechanical pressure regulators suffer from a number of problems. The spring force of the mechanical pressure regulator decreases over the life of the regulator, and it can also be affected by temperature. The effective pressure of the regulator is influenced by the flow rate through the regulator. The stiffness of the membrane of the spring force regulator changes over time as the material ages and deteriorates. As result of these effects, the set point of pressure regulator changes and will differ over time compared to the requested value. However, if the pressure regulator changes its set point, this deviation cannot be corrected by the mechanical pressure regulator. In addition, the mechanical parts are subject to the stick and slip effect because at high flow transient the friction is different. Furthermore, leaks in a line cannot be avoided because spring forced pressure regulators do not close very tightly. In addition, there is typically a need for several pressure steps for pressure reduction from a high pressure level (e.g., 700 bar) down to a low pressure level (e.g., 2 bar absolute). To realize small tolerance at the target pressure, several reduction steps have to be installed with mechanical spring forced pressure regulators.